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Uses And AbusesOf The BMI

The worldwide epidemic of obesity inchildren and young people is a

public health problem because of itsassociation with type 2 diabetes andcardiovascular disease. It is also thecause of much unhappiness. The Houseof Commons Select Committee onHealth, following the USA lead, advisedthat all children should have their bodymass index (BMI) measured on anannual basis and the result sent to eachchild’s parents. In this article I shallargue that the properties of the BMImake it a useful public health indicatorof how the obesity epidemic isprogressing, but a very poor tool foridentifying individual children at risk.

There are manydefinitions of

childhoodoverweight andobesity. Eachinvolves a measureof fatness (usuallyBMI) and a reference centile chartwhere selected centiles define cut-offsfor overweight and obesity. Statisticaldefinitions are inherently arbitrary andnone can claim to be the best inpredicting future ill health. In publichealth terms, BMI data can besummarised in several ways and thechoice is not crucial so long as there isconsistency and clarity when makingcomparisons with other studies. Inclinical terms, however, it does matter, ifthe aim is to define action points in awhole population programme, sincesmall changes in the definition maygenerate very different numbers of‘cases’.

What does BMImeasure?

The BMI is derived from the formulaweight/height2 - it is simply an index

of weight adjusted for height. It relieson two familiar measurements that canbe made on readily available equipment.However, a change in a person’s weightcould be due to changes in muscle, fator bone - but because it is(unfortunately) easierto add fat than anyother tissue, thelegitimate assumption ismade that a rise in theBMI of the populationas a whole is probablydue to increased fatness.

BMI as a measure of the fatness of anindividual has many weaknesses.

Weight can be divided into lean bodymass or fat free mass (FFM), and fatmass (FM). The ratio between themvaries according to age and gender andthere are significant ethnic differences.The ratio can also change as a result of

dieting and physicalexercise fitness training ,even though weight andtherefore BMI stay thesame. Although BMI andFM are stronglycorrelated, there is much

individual variation - a strong statisticalcorrelation between two measures in apopulation does not necessarily meanthat useful deductions can be made inindividuals. The health risks do notrelate solely to total fat mass and aremore closely correlated with intra-abdominal or visceral fat mass (VFM)which influences metabolic activity inthe liver via the portal venous system.Unfortunately BMI correlates poorlywith VFM. Furthermore, althoughobesity in childhood is associated with asignificantly increased risk of obesity inadult life, only about half of all obesechildren are obese as adults; conversely,most obese adults were not obese aschildren.

Monitoring BMI inpopulations

The BMI of the UK child andadolescent population is increasing

and there is no other convenientmeasure of fatness for populationmonitoring. Although significant errorsare likely when many different observersare involved, these will probably berandom rather than systematic. Changes

in the prevalence ofoverweight and obesityamong children andyoung people could bemonitored bymeasuring height andweight, for example at

school entry and at transfer tosecondary school, and anonymising thedata. These data would then be enteredonto a database that wouldautomatically calculate the BMI centile,relate each measurement to postcode,and compare the results with those ofprevious years. Mary Rudolf andcolleagues in Leeds have shown that theimpact of interventions would have tobe dramatic to be detected withstatistical reliability in individual schoolsbut the data could be useful informulating and evaluating local publichealth policy.

Using BMI foridentifying and advisingindividuals

Why do I argue that BMI should notbe used in the way proposed by

the House of Commons SelectCommittee? There are several reasons:

BMI is a poor measure of body fatnessand an even worse measure of the high-riskvisceral fat mass.

The interpretation of BMI measures wouldneed to be individualised for gender, ethnicityand, in older children, the stage of puberty.

There is no clear evidence as to which cut-off points on the BMI chart should trigger acommunication to parents.

Measurement errors mean that a significant

“...unfortunately BMIcorrelates poorly

with VFM...”

“BMI as a measureof fatness.. has many

weaknesses...”

Measuring Childhood ObesityMeasuring Childhood Obesity

Dr DMB Hall, Prof of Comm. PaediatricsInst. of General Practice & Primary Cared.hall@sheffield.ac.uk

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MeasuringChildhood Obesity

Following the debates about themeasuring of obesity in children, bothin and outside the pages of BACCH,Mary Jones has invited me to writeabout the issue from the perspective ofthe Department of Health (DH).

The issue of measuring childhoodobesity follows the recommendation ofthe Health Select Committee on Obesityand the publication of Choosing Health,the public health whitepaper. The NHS nowhas an LDP target for‘SHAs/PCTs to be in aposition to trackchanges in obesityprevalence’. This hasbeen deferred, for now, but theoverarching PSA target to halt the rise inchildhood obesity by 2010 still stands.

On the ground, the PCTs want toknow where to target their limitedresources. They also want to be able toevaluate the work they are alreadydoing. Epidemiologists need highquality, low-level data that will allowexamination of the causes and effects ofthe obesity ‘epidemic’. In some quartersthere is a call for annual growthmonitoring of every, individual child.

The Health Development Agencyreview of the evidence suggests thatchildhood obesity and overweight canbe tackled through a whole schoolapproach, and through family therapy, ifthe family are motivated. There is,currently, no evidence base for anindividual intervention for individualsidentified by routine measuring.

So what is the DH doing?

An Expert Advisory Group has been

brought together to inform thinking atthe DH. It includes names that will befamiliar to BACCH readers – MaryRudolph, David Hall and David Elliman.The group also has representatives fromschool nursing, education, theChildren’s Commissioner and PCTpublic health. The group feeds into thePublic Health Information andIntelligence Task Force through theChild Obesity Measures subgroup. Thetask force has a regular newsletter. Ifyou wish to join the distribution list e-mail:

The first issue that needed to bediscussed was the issueof screening individualchildren as opposed tomonitoring apopulation. The NSCmade its position clearthat an annual BMI

measure, upon which referral ofindividuals could be based, was, bydefault, a screening programme thatthey could not support. The ExpertAdvisory Group has discussed thedifference between screeningindividuals and population monitoringat length.

It became apparent that a number ofplaces around the country haveinvested time and resources indeveloping a wide variety of models formeasuring children. These places,including Birmingham, Leeds andMiddlesborough, have been generousin sharing details of their work. Modelsrange from incorporating height andweight measurement into a maths class,to sampling children across a city, andusing parent helpers to measurechildren. DH plans to evaluate thesemodels in more detail over the next fewmonths. I would be keen to hear fromother places that have experience insetting up such systems. There arelessons to be learnt, particularly around

number of children would be wronglyinformed that they were or were not at riskof being overweight or becoming obese.

We do not have any intervention to offer -even highly motivated young people who aredesperate to control their weight have greatdifficulty in doing so. It is naive to imaginethat those who have not previously beenaware of any problem will do any better.

Suitable software could overcomesome of these problems - it could for

example trap gross errors ofmeasurement or data entry andgenerate a standardised interpretationas to the significance of the results,preferably in the parents’ own language.It would of course also have toincorporate locally relevant instructionsas to where and from whom to seekfurther professional advice.

Conclusion

The BMI is the best availablepopulation marker of how the

obesity epidemic is progressing, thoughthe data may be seriously distorted ifchildren who are already overweight orobese opt out of being measured.Whole-school and whole-communityapproaches to issues of diet andexercise seem likely to be the best wayof tackling obesity but, at the level ofindividual schools, a rise in BMI couldeasily occur by chance alone and thismight demoralise a school that wasactually running a good programme.

The use of BMI as a clinical tool foridentifying individual children

would be a screening test but, as such,would fail to fulfil the standard criteriafor screening on several counts. It is ofcourse quite possible that,notwithstanding my doubts, the benefitsof such a programme might outweighthe harms but, as we have no evidenceone way or the other, any suchintervention would be an experimentand as such should be subjected to theusual ethical and governance controlsplaced on research projects.

“...an expertadvisory group has

been broughttogether...”

nicola.keay@dh.gsi.gov.uk

Measuring Childhood ObesityMeasuring Childhood Obesity

Dr Helen WaltersPublic Health Doctorhelen.walters@dh.gsi.gov.uk

many clinicians that individual children’sBMIs should not be sent to their parents– surprisingly not complained about inthe Summer News. If a school hadimplemented its Healthy School policy orwas working towards its implementation,Hall conceded, it could indeed take acomplete snapshot of all children’s BMIsat the end of every year using some kindof nationally agreed public healthminimum dataset. Whether the data weretaken anonymously or " pseudo-anonymously" - i.e. able to be linkedretrospectively to an individual child -might still be open for discussion eventhough the workshop votedoverwhelmingly for the latter.

Putting the data into anannual report would

allow a school to describeto its parents how it wasdoing as a whole. Thiswould allow Ministers to

fulfil their publicly declared commitmentto the Health Committee’s decision. Theycould declare that the Government had agood handle on local public health andthere was also an incentive on the schoolto do well. The measurements could betaken by properly trained and equippedclassroom assistants/support staff in PEtime, maths lessons or wherever andwhenever was convenient. School nursesshould not be expected to take themeasurements – there are not enoughthem to complete the job anyway – and,advantageously, taking the measurementsin class could " demedicalise " a sensitiveprocedure by making it an educationalexperience.

The published reports could not onlybe filed with the local education

authority but also with the PCT Directorof Public Health much like GP practicesfile their ‘flu uptakes with their PCT.When published at a local level, localcouncillors, PCTs, media, parents andchildren could see what was being doneby the schools in improving meals, gettingrid of vending machines etc - and couldask searching questions if they weren’t.When published at regional or national

sent home to the parents. From theletters that the Editor received she choseto reprint one in the Summer News torepresent concern that my piece wentunchallenged in a serious journal. Theauthor thought my report quite‘ludicrous’.

If you thought that might be the end ofthe matter you should know that it is

not. The ‘ludicrous’ idea is still current, isbeing addressed jointly by theDepartments of Health [DH] andEducation & Skills [DfES] and was thesubject of a June workshop called toinform the two Departments just how agroup of health specialists felt about it all.On your behalf yourEditor attended and cannow verify that not asingle word of my Springcopy was fiction and thatmany of the ChildGrowth Foundation’sviews expressed in it were being seriouslydiscussed. The conclusion to thediscussion, summarised below in aproposal made Professor Sir David Hall,has been formally submitted to theDH/DfES, each of which was wellrepresented on the day by senior civilservants, and though his proposal may besomewhat amended by the time a policyis published, he gave direction to theroute that the Government might follow.

David Hall was just one of a number ofcommunity paediatricians, public

health doctors, educationalists, primarycare workers and their unionrepresentatives invited by the Foundationto discuss the implications of yearly BMIassessment. The discussion was both fulland frank, as the saying goes, andfrequently went around in circles. It wasan interesting mix of views from peoplewho wanted to take the idea of annualBMIs forward and others who simply tookto their barricades.

In the final analysis, the proposal was a‘political’ compromise. It was voiced to

get the maximum public health benefitfrom the deal yet protect the viewpoint of

the softer aspects such as acceptabilityto children, parents, staff and schools,and stigmatisation.

Before DH can issue guidance onmeasuring childhood obesity, we needto consider a range of other issues.Work is ongoing to find answers toquestions including:

What measure to use?Who will do the measuring?Who will be measured and how

frequently?Where & how will we capture the data?

This is a complicated area. Opinions aremany and varied. Please feel free tocontact me.

Helen is compiling information for theDepartment Of Health

ANNUAL BMICHECKS STILL ONTRACK

Several BACCH readers took exceptionto the article I wrote in the Spring

News reporting the Government’sacceptance of a House of Commons’Health Committee recommendation thatyearly BMI checks for every primaryschool child be introduced and the data

“...it will have beena hot June day

worth goingthrough...”

Tam Fry,Child Growth Foundation

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BACCH News Autumn 2005BACCH News Autumn 2005

Measuring Childhood ObesityMeasuring Childhood Obesity

level, the statistics would allow PublicHealth Observatories to provide overallanalyses of how the fight against obesitywas faring. Most importantly, David Hallstated, they should choose a singledefinition of overweight/obesity from thethree currently available and stick to it.

The DH/DfES now have to decide whatto do and will take their time [maybe

2yrs] in doing so. They should also havebeen greatly helped by what they heard atthe workshop. For instance, the schoolroute had already been successfully testedin a pilot project in North Birminghamwhich is now to be rolled out across thecity. Project team members were able totalk enthusiastically about the success ofmeasuring Yr 9 children and their schooladviser saw no reason why classroommeasurements should not be carried outin every school year. They hadencountered no problem aroundweighing children as long as it was donesensitively and the children had enjoyedtheir measuring ‘lessons’. They also hadshown little inclination to stigmatise orbully fellow pupils who appearedoverweight. Projects similar to theBirmingham experience were also beingconsidered in Amersham, Blackburn withDarwen, Middlesborough and Hull.

As well as voting for pseudo-anonymityand its preference for the 91st/98th

definitions of overweight/obesity, theworkshop also voted several times onwhat the measurement frequency shouldbe. By the end of the day however thesevotes became less and less significantparticularly because they contradictedsimilar votes taken by a similar workshopin December to advise how BMI could beused to identify and audit obesity – theday on which a senior DH nutritionistannounced that annual measurementswere under review.

The DH/DFES reps in June professedthat they had learnt a lot despite –

and may be because of - the confusionthat they had sometimes witnessed. If

David Hall’s political, practical andrelatively inexpensive solution howeverallows them to advise Ministers that BMIscan be positively considered, it will havebeen a hot June day worth going through.

Update OnChildhood Obesity& Measurement OfBMI In Schools

Following the article by Tam Fry in thespring Newsletter and Helen Daly’sresponse in summer 2005, I would like toshare some information with BACCHnews readers. Firstly, I would like tooutline the historybehind the proposal tomeasure BMI in schoolchildren.

1. In 2004 the Houseof Commons HealthCommittee published itsreport on obesity. Thecommittee had taken evidence from awide range of experts and interestedparties, including Paediatricians and theChild Growth Foundation. The HealthSelect Committee recommendationnumber 58 states, ‘We recommend thatthroughout their time at school, childrenshould have their Body Mass Indexmeasured annually at school, perhaps bythe school nurse, a health visitor, or otherappropriate health professional. Theresults should be sent home in confidenceto their parents, together with, whereappropriate, advice on lifestyle, follow-up, and referral to more specialisedservices. Where appropriate, BMI

measurement could be carried outalongside other health care interventionswhich are delivered at school, forexample inoculation programmes. Carewill need to be taken to avoidstigmatising children who are overweightor obese, but given that researchindicates that many parents are nolonger even able to identify whether theirchildren are overweight or not, thisseems to us a vital step in tacklingobesity.’

2. The Department of Health’s responseto the Health Select Committee repeatedthe recommendation and also stated that‘to support the development of local datasources, and improvements in dataquality, the DH will continue to workclosely with the DfES to developappropriate systems for recording lifestylemeasures, for example obesity throughweight and height measurements, amongschool age children.’

3. In the Chief Medical Officers updatein March 2005 the CMO wrote ‘Other

recommendationsaimed at childreninclude having theirBMI measuredannually at school withthe result sent toparents with advice orreferral to a specialised

service and promoting practical cookeryskills to school children’.

Many of us were alarmed at this poorlythought through statement and have beenworking to limit the potential harm frominappropriate implementation of whatwould effectively be a screeningprogramme. Letters have gone to theCMO explaining our concern.

4. ‘Delivering choosing health’ – theimplementation plan for the public healthwhite paper, states ‘DH will continue towork closely with DfES to developappropriate systems for recording lifestylemeasures, for example obesity through

“I am delighted to seeobesity so high on theagenda, but there arestill many unanswered

questions...”

Measuring Childhood ObesityMeasuring Childhood Obesity

Dr Penny GibsonConsultant Community Paediatrician &RCPH Advisor in childhood obesitypenny.gibson@shb-tr.nhs.uk

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weight and height measurements, amongschool age children.’

5. The government is now committed toimproving public health and as part ofdoing this there is a public serviceagreement (PSA) between the Treasury andthe DH setting objectives. Objective 1 is;

‘Improve the health of the population. By2010 increase life expectancy at birth inEngland to 78.6 years for men and 82.5years for women.’

One of the eight specific targetsunderpinning this overarching objective is:

‘Tackle the underlying determinants of illhealth and health inequalities by halting theyear on year rise in obesity among childrenunder 11 by 2010, in the context of abroader strategy to tackle obesity in thepopulation as a whole.’

So the DH will beexpecting PCTs tocontribute to thetreatment and preventionof childhood obesity.

I am delighted to seeobesity so high on theagenda but there are stillmany unansweredquestions. For example, it is not yet beendecided how success with these targetswill be measured. How will individualPCTs, the DH or the government knowwhether the target has been met? Theobvious answer seems to be that we mustmake sure that children are measured.

If we are gong to measure children weneed to decide what the main purpose is

As a source of national dataAs a source of local dataAs a screening process

The last possibility is what is implied inthe health select committeerecommendation. However measurementof BMI is a very poor screen for a largenumber of reasons.

BMI is not be a very good measure ofobesity in individual children and needscareful interpretation when used clinically

The cut-offs for definition of overweightand obesity are not agreed

We do not have widely available, effectiveservices for the treatment of obesity

We have no idea of the harm that may bedone by identifying children who are obeseand being unable to support or treat themadequately.

The measuring process itself may causeharm to some children eg by stigmatisation

On the 17th June 2005 Tam Fry hosted aworkshop ‘Annual BMI Checks inschools’. A variety of methods ofmeasuring children were discussed. I wasparticularly impressed by a presentationby Christina Routh, Specialist Registrar in

Birmingham. They haddesigned and carried outanonymous monitoring inseven schools, during anumeracy lesson for Year 5children (9-10 years old).The process was donesensitively, with carefulplanning of the detail to

allow completely anonymous measuringand recording.

We now have the problem of politicalexpectation of implementation of annualmeasuring in primary age childrenwithout the backing of the nationalscreening committee and many healthprofessionals. The Department of Healthhave appointed Dr Helen Walters, a PublicHealth doctor, to take a lead on resolvingthe measuring problem. Dr Walters heldan expert advisory group meeting on 29thJune. Community Paediatrics was wellrepresented by Professor Sir David Hall,Dr David Elliman and Dr Penny Gibson.David Hall crystallised the view of thepaediatricians present when he describedour role there as being ‘damage

limitation’. We are all very keen to seethat the political imperative to measure isimplemented in a way that does minimalor no harm whilst providing usefulinformation. The expert advisory grouplooked at three main possibilities.

Screening: measuring every child toenable identification of obese children andoffer them an intervention

Sampling: measuring a sample of childrento give a picture of the whole population

Anonymous monitoring: measuring everychild and collating the data anonymously

There will need to be a lot morediscussion before implementation ofwhichever is chosen. The most pragmaticcompromise at the moment seems to beanonymous monitoring. There will beplenty more discussion, so please do letme know your views.

Meanwhile NICE is in the process ofdeveloping guidelines for the treatmentand prevention of adult and childhoodobesity. These are due to be ready for2007. There will be a short consultationperiod in February 2006. It is very likelythat recommendations will have asignificant impact on Paediatricians! If youwould like to comment on the draftguidelines please let me know.

“The mostpragmatic

compromise seemsto be anonymous

monitoring...”

Measuring Childhood ObesityMeasuring Childhood Obesity

Autumn 2005

V I E W S F R O M :

Prof David Hall,

Helen Waltersat the Dept of Health,

Tam Fry of theChild Growth Foundation

and a letterfrom Penny Gibson

V I E W S F R O M :

Prof David Hall,

Helen Waltersat the Dept of Health,

Tam Fry of theChild Growth Foundation

and a letterfrom Penny Gibson

SUPPLEMENTSUPPLEMENTMeasuring Childhood ObesityMeasuring Childhood Obesity

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